In vivo imaging of the surface of the nervous system and its fluid cavities has long been a goal of neuroradiologists. In many cases this requires contrast enhancement of the cerebrospinal fluid (CSF) spaces. Unfortunately, there have been no practical and safe contrast agents available in the past. However, recent advances in the development of water soluble contrast agents now raise the possibility of direct delineation of the brain surfaces and its cavities. However, even the newest and most benign radiographic contrast agets produce neurotoxic effects when directly applied to the central nervous system (CNS). In order to avert the toxic effects of contrast agents, it would be helpful to understand the etiology of these adverse effects. One of the major clinical sequela of directly applying contrast agents to the CNS is seizures. Thre is little information as to how these drugs induce seizures. This research will approach that problem using two methodologies. First, the mechanism of spinal seizure activity will be investigated using the isolated cat spinal cord. This preparation allows the recording of dorsal and ventral root electrical activity as well as single cell analysis of spinal neurons. The neurophysiologic effects of radiographic contrast agents on spinal roots, single spinal neurons and groups of spinal neurons in excitatory and these drugs will be investigated. In addition, the intracellular effects of these drugs will be investigated by use of an invertebrate nervous system, the abdominal ganglia of Aplysia, which allows more extensive evaluation of membrane properties and synaptic events. Using these techniques, the mechanism of the neurotoxic effects reflected as increased CNS electrical activity will be better understood. From this information, alterations of the chemistry of these compounds or diminution of their toxic effects by combination with other drugs will be proposed.